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<H3>group2ndx command 
</H3>
<P><B>Syntax:</B>
</P>
<PRE>group2ndx file group-ID ... 
</PRE>
<UL><LI>file = name of index file to write out 

<LI>zero or more group IDs may be appended 


</UL>
<P><B>Examples:</B>
</P>
<PRE>group2ndx allindex.ndx
group2ndx someindex.ndx upper lower mobile 
</PRE>
<P><B>Description:</B>
</P>
<P>Write a Gromacs style index file in text format that associates atom IDs
with the corresponding group definitions. This index file can be used 
with in combination with Gromacs analysis tools or to import group
definitions into the <A HREF = "fix_colvars.html">fix colvars</A> input file.
</P>
<P>Without specifying any group IDs, all groups will be written to the index
file. When specifying group IDs, only those groups will be written to the
index file. In order to follow the Gromacs conventions, the group <I>all</I>
will be renamed to <I>System</I> in the index file.
</P>
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<P><B>Restrictions:</B>
</P>
<P>This command requires that atoms have atom IDs, since this is the
information that is written to the index file.
</P>
<P>This fix is part of the USER-COLVARS package.  It is only enabled if
LAMMPS was built with that package.  See the <A HREF = "Section_start.html#start_3">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "group.html">group</A>, <A HREF = "dump.html">dump</A>, <A HREF = "fix_colvars.html">fix colvars</A>
</P>
<P><B>Default:</B> none
</P>
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